Re: Solibs and objfile BFD ownership

[Paul Pluzhnikov <ppluzhnikov@google.com>]

[-- Attachment #1: Type: text/plain, Size: 974 bytes --]

On Tue, Jul 28, 2009 at 8:40 AM, Daniel Jacobowitz<drow@false.org> wrote:

>  clear_solib ();
>  objfile_purge_solibs ();
>
> The problem with doing things in this order is that both the solib and
> the objfile have a reference to the same BFD.  The solib is
> responsible for releasing it (OBJF_KEEPBFD).  arm_objfile_data_cleanup
> accesses objfile->obfd during free_objfile, to find the number
> of sections; at that point it's already been free'd.

That is a problem.

> Any thoughts?

There doesn't appear to be a correct order of destruction :-(

Attached patch restores the original order, while still keeping
solib_unloaded observers from accessing danglig objfiles.

I do not know if there is a better way to fix this.

Tested on Linux/x86_64 with no new regressions.

Thanks,
-- 
Paul Pluzhnikov

2009-07-29  Paul Pluzhnikov  <ppluzhnikov@google.com>

	* solib.c (clear_solib): Rename to clear_solib_1
	(clear_solib): New function.
	(no_shared_libraries): Adjust.

[-- Attachment #2: gdb-clear-solib-20090729.txt --]
[-- Type: text/plain, Size: 2102 bytes --]

Index: solib.c
===================================================================
RCS file: /cvs/src/src/gdb/solib.c,v
retrieving revision 1.122
diff -u -p -u -r1.122 solib.c
--- solib.c	17 Jul 2009 17:08:23 -0000	1.122
+++ solib.c	29 Jul 2009 23:39:11 -0000
@@ -893,10 +893,8 @@ solib_name_from_address (CORE_ADDR addre
   return (0);
 }
 
-/* Called by free_all_symtabs */
-
-void
-clear_solib (void)
+static void
+clear_solib_1 (int notify_observers)
 {
   struct target_so_ops *ops = solib_ops (target_gdbarch);
 
@@ -928,7 +926,8 @@ clear_solib (void)
     {
       struct so_list *so = so_list_head;
       so_list_head = so->next;
-      observer_notify_solib_unloaded (so);
+      if (notify_observers)
+        observer_notify_solib_unloaded (so);
       if (so->abfd)
 	remove_target_sections (so->abfd);
       free_so (so);
@@ -937,6 +936,15 @@ clear_solib (void)
   ops->clear_solib ();
 }
 
+/* Called by free_all_symtabs */
+
+void
+clear_solib (void)
+{
+  clear_solib_1 (1);
+}
+
+
 /* GLOBAL FUNCTION
 
    solib_create_inferior_hook -- shared library startup support
@@ -1018,13 +1026,20 @@ sharedlibrary_command (char *args, int f
 void
 no_shared_libraries (char *ignored, int from_tty)
 {
-  /* The order of the two routines below is important: clear_solib notifies
-     the solib_unloaded observers, and some of these observers might need
-     access to their associated objfiles.  Therefore, we can not purge the
-     solibs' objfiles before clear_solib has been called.  */
+  struct so_list *so = so_list_head;
+
+  /* We notify all solib_unloaded observers before destroying any objfiles,
+     because some observers need access to their associated objfiles.  */
+
+  for (so = so_list_head; so; so = so->next)
+    observer_notify_solib_unloaded (so);
+
+  /* The order of the two routines below is important: clear_solib_1
+     will free/close objfile->obfd (solib owns it), but objfile_purge_solibs
+     needs access to it (at least on ARM, see arm_objfile_data_cleanup).  */
 
-  clear_solib ();
   objfile_purge_solibs ();
+  clear_solib_1 (0);
 }
 
 static void